Engineering Negative Differential Conductance with the Cu(111) Surface State

TL;DR

This study demonstrates how electron tunneling from a C60-terminated tip into Cu(111) surface states can produce tunable negative differential conductance, influenced by molecular orientation and barrier thickness, revealing symmetry effects.

Contribution

It introduces a method to engineer negative differential conductance using molecular tips and surface state symmetry matching in low-temperature STM experiments.

Findings

NDC observed between C60 orbital and Cu surface states

NDC can be tuned or extinguished by barrier thickness and C60 orientation

Symmetry matching explains orientation dependence of NDC

Abstract

Low-temperature scanning tunneling microscopy and spectroscopy are employed to investigate electron tunneling from a C60-terminated tip into a Cu(111) surface. Tunneling between a C60 orbital and the Shockley surface states of copper is shown to produce negative differential conductance (NDC) contrary to conventional expectations. NDC can be tuned through barrier thickness or C60 orientation up to complete extinction. The orientation dependence of NDC is a result of a symmetry matching between the molecular tip and the surface states.